Neisseria lactamica Controlled Human Infection Model

Controlled human infection model of Neisseria lactamica in late pregnancy investigating mother-to-infant transmission in the UK: a single-arm pilot trial

BACKGROUND

The infant respiratory microbiome is derived largely from the mother and is associated with downstream health and disease. Manipulating maternal respiratory flora peripartum to influence the infant microbiome has not previously been investigated. Neisseria lactamica is a harmless pharyngeal commensal that correlates inversely with Neisseria meningitidis carriage and disease. Intranasal N lactamica inoculation is a safe and well characterised controlled human infection model (CHIM) in non-pregnant healthy adults. We hypothesised that N lactamica inoculation in pregnancy induces mother-to-infant N lactamica transmission postnatally.

METHODS

In this single-arm trial, 21 healthy pregnant female participants aged 18 years or older were inoculated at 36-38 weeks' gestation with 105 colony-forming units of N lactamica Y92-1009 at University Hospital Southampton Clinical Research Facility, Southampton, UK. N lactamica selective culture, genome sequencing, and serological testing were performed on maternal and infant oral, nasopharyngeal, breastmilk, and serum samples over 15 weeks postpartum. Seven female participants naturally colonised with N lactamica at baseline were followed up, but not inoculated. Oral samples were obtained from 12 cohabiting siblings younger than 5 years. The primary endpoint was infant N lactamica colonisation. This study was registered with ClinicalTrials.gov, NCT04784845, and is now complete.

FINDINGS

Between Oct 25, 2021, and March 7, 2022, 31 adult female participants (median age 33·5 years [range 23·1-39·9]; 26 [84%] were White, British) were screened and enrolled, of whom seven were already colonised with N lactamica. After exclusion of three participants, 21 participants were inoculated, of whom 15 (71%) became N lactamica-colonised, and no sustained N lactamica Y92-1009 transmission to their infants was observed. Conversely, non-Y92-1009 N lactamica strain sharing was observed in four (57%) of seven uninoculated mother-sibling pairs, and Moraxella catarrhalis strain sharing in nine (38%) of 24 mother-infant pairs completing the study. Anti-N lactamica serum IgG titres increased in seven (88%) of eight N lactamica Y92-1009-colonised female participants, but none of their infants (where paired sera were available). There were no serious adverse reactions to the inoculum.

INTERPRETATION

As the world's first perinatal CHIM, this trial demonstrates that this model in pregnancy is feasible, and that N lactamica Y92-1009 can safely and efficiently colonise pregnant individuals. Lack of sustained mother-to-infant N lactamica transmission, despite evidence supporting mother-to-infant M catarrhalis and sibling-to-mother N lactamica transmission, challenges conventional perceptions of infants as passive recipients of maternal microbes, suggesting that respiratory commensal transmission is selective and microbe-specific.

FUNDING

Medical Research Council and National Institute for Health Research Southampton Biomedical Research Centre.

A Questionnaire-based Study Exploring Participant Perspectives in a Perinatal Human Challenge Trial

BACKGROUND

Pregnant women have historically been excluded from most medical research, including human challenge studies. The proof-of-concept Lactamica 9 human challenge study investigated whether nasal inoculation of pregnant women with commensal bacteria leads to horizontal transmission to the neonate. Given the unique practical and ethical considerations of both human challenge studies and interventional research involving pregnant women and their newborns, we sought to investigate the motivations, concerns and experiences of these volunteers.

METHODS

Pre- and post-participation questionnaires were given to all participants in the Lactamica 9 study. These fully anonymized qualitative and Semi-quantitative questionnaires used forced Likert scales, word association and free-text questions.

RESULTS

Pre- and post-participation questionnaires were completed by 87.1% (27/31) and 62.5% (15/24) of eligible participants, respectively. Almost all pre-participation respondents agreed with altruistic motivations for participation, and most concerns were related to discomfort from study procedures, with few concerned about the theoretical risks of inoculation to themselves (5/27; 18.5%) or their baby (6/27; 22.2%). Participants most frequently associated the study intervention with the terms "bacteria," "natural," "protective" and "safe." For the post-participation questionnaire, 93.3% (14/15) found all study procedures acceptable, and qualitative feedback was almost entirely positive, with particular emphasis on the research team's flexibility, approachability and friendliness.

CONCLUSIONS

The successful completion of the Lactamica 9 study demonstrates that human challenge research in healthy pregnant women can be acceptable and feasible. Participants' initial concerns of potential discomfort were outweighed by predominantly altruistic motivations and perception of the intervention as "natural."

Effect of colonisation with Neisseria lactamica on cross-reactive anti-meningococcal B-cell responses: a randomised, controlled, human infection trial

BACKGROUND

Pharyngeal colonisation by the commensal bacterium Neisseria lactamica inhibits colonisation by Neisseria meningitidis and has an inverse epidemiological association with meningococcal disease. The mechanisms that underpin this relationship are unclear, but could involve the induction of cross-reactive immunity. In this study, we aimed to evaluate whether colonisation with N lactamica induces N lactamica-specific B-cell responses that are cross-reactive with N meningitidis.

METHODS

In this randomised, placebo-controlled, human infection trial at University Hospital Southampton Clinical Research Facility (Southampton, UK), healthy adults aged 18-45 years were randomly assigned (2:1) to receive intranasal inoculation with either 105 colony-forming units of N lactamica in 1 mL phosphate-buffered saline (PBS) or 1 mL PBS alone. Participants and researchers conducting participant sampling and immunological assays were masked to allocation. The primary endpoint was the frequency of circulating N lactamica-specific plasma cells and memory B cells after N lactamica inoculation (day 7-28) compared with baseline values (day 0), measured using enzyme-linked immunospot assays. The secondary endpoint was to measure the frequency of N meningitidis-specific B cells. In a second study, we measured the effect of duration of N lactamica colonisation on seroconversion by terminating carriage at either 4 days or 14 days with single-dose oral ciprofloxacin. The studies are now closed to participants. The trials are registered with ClinicalTrials.gov, NCT03633474 and NCT03549325.

FINDINGS

Of 50 participants assessed for eligibility between Sept 5, 2018, and March 3, 2019, 31 were randomly assigned (n=20 N lactamica, n=11 PBS). Among the 17 participants who were colonised with N lactamica, the median baselines compared with peak post-colonisation N lactamica-specific plasma-cell frequencies (per 105 peripheral blood mononuclear cells) were 0·0 (IQR 0·0-0·0) versus 5·0 (1·5-10·5) for IgA-secreting plasma cells (p<0·0001), and 0·0 (0·0-0·0) versus 3·0 (1·5-9·5) for IgG-secreting plasma cells (p<0·0001). Median N lactamica-specific IgG memory-B-cell frequencies (percentage of total IgG memory B cells) increased from 0·0024% (0·0000-0·0097) at baseline to 0·0384% (0·0275-0·0649) at day 28 (p<0·0001). The frequency of N meningitidis-specific IgA-secreting and IgG-secreting plasma cells and memory B cells also increased signficantly in participants who were colonised with N lactamica. Upper respiratory tract symptoms were reported in ten (50%) of 20 participants who were inoculated with N lactamica and six (55%) of 11 participants who were inoculated with PBS (p>0·99). Three additional adverse events (two in the N lactamica group and one in the PBS group) and no serious adverse events were reported. In the second study, anti-N lactamica and anti-N meningitidis serum IgG titres increased only in participants who were colonised with N lactamica for 14 days.

INTERPRETATION

Natural immunity to N meningitidis after colonisation with N lactamica might be due to cross-reactive adaptive responses. Exploitation of this microbial mechanism with a genetically modified live vector could protect against N meningitidis colonisation and disease.

FUNDING

Wellcome Trust, Medical Research Council, and NIHR Southampton Biomedical Research Centre.

Controlled human infection with Neisseria lactamica in late pregnancy to measure horizontal transmission and microbiome changes in mother-neonate pairs: a single-arm interventional pilot study protocol

INTRODUCTION

Infant upper respiratory microbiota are derived partly from the maternal respiratory tract, and certain microbiota are associated with altered risk of infections and respiratory disease. Neisseria lactamica is a common pharyngeal commensal in young children and is associated with reduced carriage and invasive disease by Neisseria meningitidis. Nasal inoculation with N. lactamica safely and reproducibly reduces N. meningitidis colonisation in healthy adults. We propose nasal inoculation of pregnant women with N. lactamica, to establish if neonatal pharyngeal colonisation occurs after birth, and to characterise microbiome evolution in mother-infant pairs over 1 month post partum.

METHODS AND ANALYSIS

20 healthy pregnant women will receive nasal inoculation with N. lactamica (wild type strain Y92-1009) at 36-38 weeks gestation. Upper respiratory samples, as well as optional breastmilk, umbilical cord blood and infant venous blood samples, will be collected from mother-infant pairs over 1 month post partum. We will assess safety, N. lactamica colonisation (by targeted PCR) and longitudinal microevolution (by whole genome sequencing), and microbiome evolution (by 16S rRNA gene sequencing).

ETHICS AND DISSEMINATION

This study has been approved by the London Central Research Ethics Committee (21/PR/0373). Findings will be published in peer-reviewed open-access journals as soon as possible.

TRIAL REGISTRATION NUMBER

NCT04784845.